1. Technical Field
The present invention relates to an offset cancelling circuit which is used for adjustment of an output or the like of a Hall element.
2. Related Art
In recent years, image capturing devices such as a digital still camera and a digital video camera realize higher image quality by increasing the number of pixels of an image capturing element of the image capturing device. On the other hand, as another method for realizing higher image quality of the image capturing device, it is desired to equip the image capturing device with a vibration absorption control circuit having a shake correction function in order to prevent shaking of imaging target caused by shaking of the hand holding the image capturing device.
A vibration absorption control circuit for shake correction receives a signal from a gyro sensor which detects an angular velocity component generated by vibration of the image capturing device, and drives optical components such as a lens and an image capturing element according to the received signal, to prevent shaking of the imaging target. With such a configuration, even if the image capturing device vibrates, the component of the vibration is not reflected in the obtained image signal, and a high-quality image signal having no image shaking can be obtained.
In this process, a Hall element is used for detecting a position of the optical component such as the lens which is driven. As shown in FIG. 8, an equivalent circuit of the Hall element 10 can be represented as a bridge circuit of resistors R1˜R4. Because of this, an output signal of the Hall element 10 includes an offset component due to influences of variations in the resistors, according to a combination of a terminal on which a power supply voltage Vcc is applied and a terminal from which the output signal is extracted.
In consideration of this, an offset cancelling circuit is used which applies a voltage such that currents flowing in the Hall element 10 differ by 90°, and adds and calculates an average of the output voltages. When the current flowing in the Hall element 10 is changed by 90°, the offset of the output voltage of the Hall element 10 occurs in an opposite direction, and thus the offset value of the output voltage of the Hall element 10 is cancelled.
The offset cancelling circuit of the related art assumes that no change occurs in the resistors R1˜R4 of the equivalent circuit of the Hall element in a first state and a second state.
However, in a normal Hall element, there is a voltage dependency of the resistors R1˜R4. As shown in FIG. 9, the resistors R1˜R4 are represented as an N-type semiconductor element in which a P-type substrate is grounded. When the terminal A is grounded, Vcc is applied to the terminal B, and Vcc/2 is applied to the terminal D as shown in FIG. 9, there is a difference in a depth in a depletion layer (channel) X formed in the element, and thus the resistors R1˜R4 have a voltage dependency. In other words, the values of resistors R1˜R4 would vary depending on the combination of the voltages applied to the terminals A˜D.
In such a case, the offset value of the output voltage of the Hall element cannot be accurately cancelled with the offset cancelling circuit of the related art.